1. Field of the Invention
The present invention concerns a method and an apparatus to visualize nuclear medicine data from different modalities, in a single image.
2. Description of the Prior Art
The following definitions, acronyms and abbreviations are used herein:
PET Positron emission tomography
SPECT Single-photon emission tomography
NaF Sodium fluoride
NM Nuclear medicine
MIP Maximum intensity projection
CT Computed tomography
FDG Flodeoxyglucose
MPR Multi-planar reformatting/reconstruction/rendering
MRI Magnetic resonance imaging
RGBA Color representation as red/green/blue and alpha (opacity)
LUT Look-up table: in this context, a LUT contains the transformation from observed values (here, uptake values) to visualized pixel/voxel values, often encoded as RGBA.
VOI Volume of Interest
HSV Hue Saturation Value
With the clinical availability of more and more nuclear imaging tracers, a detailed examination of a patient may combine information collected from image data acquired with more than one radioisotope. For instance a combination of 18F-FDG and 18F—NaF PET/CT increases the sensitivity for detection of osseous lesions compared to 18F-FDG PET/CT alone, independent of whether both scans were performed as separate studies or as a single study with simultaneous tracer injection, as described in Lin et al., “Prospective comparison of combined 18F-FDG and 18F—NaF PET/CT vs. 18F-FDG PET/CT imaging for detection of malignancy,” Eur J Nucl Med Mol Imaging 2012, 39, pp. 262-270. While in this example 18F—NaF PET/CT provides particular advantages in detecting bone metastasis (See Hetzel et al., “F-18 NaF PET for Detection of Bone Metastases in Lung Cancer: Accuracy, Cost-Effectiveness, and Impact on Patient Management,” Journal of Bone and Mineral Research 2003, 18(12), pp. 2206-2214), it can be expected that other tracers will prove themselves useful for detecting pathologies in other structures/organs. Hence, a combination of more than one tracer will, for certain medical questions, reveal more information to the reading physician than a single tracer alone can.
The increasing amount of information for the reading physician makes it at the same time more and more difficult to get a fast overview of the patient's condition and to focus on diagnostically relevant organs and structures. This is particularly true if more than one scan with multiple radioisotopes has been acquired.
Currently multiple studies with different tracers are typically reviewed individually or side-by-side. For this purpose, a LUT, which may be a color LUT, is often applied to the functional data and the result is visualized as overlay on the corresponding anatomical data, if available. In the following, such visualization is referred to as fused imaging, or fusion.
Furthermore, 3D visualizations may be rendered using, for instance, a maximum-intensity-projection (MIP) to display an overview of the NM data.
In the case of multiple-tracers being combined in one study, no conventional dedicated rendering techniques are currently known.
That is, similar to above, one LUT is applied for fused imaging or to generate a MIP. In that case the correlation between each tracer and the observed uptake is lost. Note that cases where uptake can be associated to the individual tracer, e.g., SPECT imaging of tracers emitting photons of different energies, can be regarded as the first use-case that includes multiple studies.